Absorbent landscapes

Overview

Landscape alternatives capture rainfall in leafy green foliage, with the intention of increasing infiltration, filtration, and evapotranspiration of rainfall and runoff. Well-designed landscape alternatives require little maintenance and less irrigation after establishment than turf.

Healthy, uncompacted soil provides important stormwater management functions including infiltration and temporary storage of runoff, filtration of suspended sediments, adsorption and biological decomposition of pollutants and moderation of peak stream flows and temperatures. Healthy soils also support vigorous plant growth that intercepts rainfall, returning much of it to the atmosphere through evaporation and transpiration. Standard construction practices involve removing and stockpiling topsoil during clearing and grading, compacting subsoil and replacing a shallow layer of the stockpiled site topsoil, typically 10 to 15 cm deep, on top of the compacted subsoil at the end of construction. This typically produces a poor quality growing environment that requires excessive irrigation and fertilizer applications to establish plantings, raising the potential for these pervious areas to be a source of contaminated runoff during storm events.

A simple, inexpensive lot level stormwater management practice is the application of a deeper than standard layer of high quality topsoil in pervious landscaped areas, especially those that will receive roof runoff from downspouts. This practice is of particular interest because at the end of construction work there is always a surplus of topsoil from clearing and grading that otherwise must be hauled away at a cost to the developer. The practice of adjusting grading of landscaped areas, scarifying the subsoil to reverse compaction, and applying a deeper layer of organic topsoil has the potential to reduce costs associated with having to haul it away. It also has the potential to absorb, infiltrate and evapotranspire a greater amount of stormwater than standard landscaping practices, thereby providing runoff reduction benefits. Amending poor quality topsoil or compacted subsoil with compost increases moisture and pollutant retention capacity and permeability, and reduces bulk density and erosivity. In addition, this practice also provides a better growing environment for grass, shrub and tree plantings, requiring less irrigation and fertilizer to become established than plantings in more shallow, unimproved topsoil overlying compacted subsoil.

Landscape alternatives allow homeowners to customize their property’s landscape to their liking. A guiding principle when designing landscape alternatives is “the right plant for the right place”. Using both native and non-native plants is acceptable as long as the non-native plants are not invasive and do not require frequent watering. Various landscape alternatives are available, including:

Xeriscaping

Xeriscaping refers to landscaping, plantings and gardening practices that reduce or eliminate the need for watering by selecting plants based on their ability to survive with little water. Synonymous with water conservation, xeriscaping was originally promoted in areas with perennial water shortages. Additional benefits include reducing water bills, lowering maintenance requirements, and better plant survival rates and aesthetics during drought periods. Xeriscaping can be used on a lot-by-lot basis or in combination with larger residential LID programs. The Region of Peel’s Fusion Landscaping® program is an example of this.

Tree Clusters

Tree clusters are another residential landscape alternative. Tree clusters improve water quality, generate organic soils, absorb greenhouse gases, and provide shade for homes. Tree clusters require larger lot sizes, preferably with no overhead wires. They can be planted as standalone features or as part of a larger residential LID landscape.

Topsoil

STEP have a guide to amending and improving topsoil to improve the water retention capacity and promote healthy vegetation. I can be found here on our main website.

Topsoil and Soil Amendment Calculator Spreadsheet Tool, V 2.0

Materials

• Topsoil
• Sand
• Compost
• Organic matter

See also

• Better site design
• Grading
• Downspout disconnection
• Vegetated filter strips
• Enhanced swales

The technique of removing pollutants from runoff as it infiltrates through the soil.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

The attachment of gas, vapour or dissolved matter onto the surface of solid materials.

Abiotic transfer of water vapour to the atmosphere.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

The treatment of urban runoff as close to the source area as possible through application of small scale stormwater management practices on individual properties that are linked to downstream conveyance and end-of-pipe practices.

Decayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil.

Defined as those plants (including grasses, herbaceous species, shrubs, vines and trees) that have historically existed within a particular area. Native plants have co-evolved with the local ecosystems and natural processes.

Reduction in applied water due to more efficient water use such as implementation of Urban Best Management Practices or Agricultural Efficient Water Management Practices. The extent to which these actions actually create a savings in water supply depends on how they affect net water use and depletion.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Sustainable Technologies Evaluation Program